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Tuesday, July 28, 2009

Dialing In Skin Tone

A wedding professional has some sage advice and techniques for mastering elusive skin tones

This Article Features Photo Zoom

Here, again, we have an image that’s tough to get a handle on with the histogram. The whites of the veil are quite hot, but the skin tones look very good.

The problem for digital photographers lies in the size of the bucket—as more pixels are placed on the face of a sensor, the buckets have to get smaller and smaller to accommodate all the buckets. When a bucket fills up, the resulting part of the image is clipped to white (meaning it loses detail) even though there may be more photons available. A photo carries information, so a bucket that fills at 10 photons clips to white before a bucket that fills with 20.

This is an oversimplification of the process, of course, but it illustrates one of the common problems with digital photography—as more and more pixels get pushed onto digital sensors, the range of detail available increases while the dynamic range decreases. Since the range of tones is limited by the size of those photo buckets, improper exposure can dramatically limit the amount of contrast in an image.

Rules Of Thumb
Many photographers use a rule of thumb for shooting digital that’s slightly inaccurate, but it’s a good on-the-fly guide for quick digital photography: Shoot your images slightly underexposed. The reason for this logic lies again in those buckets of photons—if you overexpose your images, you’re going to clip your image and lose detail in the highlights (and the human eye is better at seeing details in highlights than in shadows). If you’re slightly underexposed, you’re much more likely to preserve the full range of tones in your image.

However, this rule causes issues when shooting particularly dark scenes, where you don’t have bright highlights and will instead lose detail in the shadows. Ideally, you should meter each image as close to the edge of your highlight exposure without clipping anything.

If the brightest tone in your image is a midtone, then you’re best to meter and expose for that as your highlight, since that will distribute the greatest range of tones across the rest of the image.

Most photographers do this by looking at the in-camera histogram of their image and metering so that the right edge of the histogram tapers off at the edge of the clipping point. However, there’s a caveat to this. Many cameras display their histogram information from the JPEG settings, and JPEG images can clip data before the RAW file would lose the data. That’s why it’s a good idea to shoot weddings and many other subjects using a handheld light meter.